The present invention relates to a sputtering target in the form of a ring and including a ring shaped concave sputtering surface lying between an inner and outer rim of a target area.
Ring shaped targets consist of the material to be sputtered within a cathode sputtering apparatus, for depositing a layer on substrate surfaces in the apparatus. The layer consists of the target material or, in the case where a chemically active gas is present in the sputtering apparatus, a chemical compound consisting of elements of the target material and of the active gas is deposited as the layer. Such targets are used in sputtering sources and especially in magnetic field supported sputtering sources, such as magnetrons. Ring shaped targets are especially suited for applications where the substrate to be sputtered is placed statically in front of the sputtering source and where a homogeneous coating is to be deposited. Ring shaped arrangements also allow the use of especially thick targets as the necessary constructive measures so that ring shaped arrangements for the generation of suitable magnetic field configurations can be realized more easily. Magnetic poles and magnetic field generating devices, for instance, can be placed easily on the inner and outer sides of the ring shaped targets, as there is a hollow space within the central area of the ring target which can be used for such structures. The central area of the usual planar target, however, is not available for this purpose.
A known cathode sputtering device with a ring target is, for instance, described in the German Patent Specification DE 40 42 286. To reach long operating hours for the sputtering device, thick targets are preferred. With thick targets, however, there is the problem that the continuing erosion strongly changes the target surface due to the progressing erosion of the target which leads to a different operating behavior. Problems can arise due to the fact that, after a certain period, the surface is no longer evenly sputtered at various positions of the eroded target. There can even be a redeposition of the sputtered target material which then leads to an unwanted layer on the target surface. The unwanted layer can lead to chip-offs which can make the coated substrate unusable. Other possible problems are contamination or instabilities with arcing during the sputtering operation. This can even lead to a breakdown of the entire sputtering apparatus. The problem is partly solved by laterally lifting the poles as described in German Patent Specification DE 40 42 286. Up to a certain degree, this also optimizes target utilization. Another measure to solve these problems is suggested in this German Patent Specification. It consists of giving the sputtering surface a certain form. The main part is formed as a flat recess enclosed by two concentric prominences whose walls stand at a preset angle, ranging between 30 to 70 grades. This measure prevents the deposition of the target material on the wall surfaces of the target prominences and at the same time it maintains the advantages of the hollow magnetron, i.e. the high utilization rate of the target material. With this construction it was found that the redeposition on the lateral wall surfaces cannot be completely prevented on the whole of the sputtering surface during the entire target lifetime. In addition, with this construction the utilization rate of the target was restricted to a certain maximum value. The target also could only be used with a sufficient operating safety as long as no important redepositions took place or as long as the layer was not damaged by chip-offs. This, in addition, restricted the utilization rate of the device.